Frank Gehry stands in front of his Serpentine pavilion, which will be completed in mid-July. Photograph: Nils Jorgenson / Rex

The Bilbao effect has landed in that well-known centre of urban deprivation and grime, the smooth green lawns of Kensington Gardens. The architect Frank Gehry has been headhunted by city authorities all over the world since 1997, when his gleaming, wriggling Guggenheim Bilbao museum was credited with transforming the economy of the rundown post-industrial Spanish port. ("That's bullshit," he said modestly today.) Now he is within days of completing his first building in England, the temporary summer pavilion for the Serpentine gallery, which is becoming one of the starriest and worst paid commissions in the arts world.

Every year, some world-renowned architect whimpers on learning that Julia Peyton-Jones, the gallery's famously formidable director, is on the phone. It has already happened to Zaha Hadid, Daniel Libeskind, Toyo Ito, Rem Koolhaas and Oscar Niemeyer. The results have been spectacular though. Richard Rogers, though probably feeling blessed that he's ineligible - to qualify, the designer must never have completed a building in England - says: "I couldn't single one out that I have liked more than the others - they have all been masterpieces."

This year it was Gehry's turn; apart from an aborted seaside tower project for Hove, he has never worked in England, and his only British building is the cancer care Maggie's Centre in Dundee.

Resistance is futile. Hiding under the desk, or merely claiming to be insanely busy - Gehry is also working on projects in Las Vegas, Princeton, Napa Valley, Panama and Spain - doesn't help.

"It's an expensive yes, I can tell you," he groaned yesterday. "Will I get into heaven for that?"

"Absolutely," Peyton-Jones assured him, "and the angels will serenade you on your arrival."

In the mere six months between first pencil scribble to next week's opening night concert, including getting planning permission, Gehry designed a spectacular tangle of glass, Douglas fir timber and steel, supported on four massive columns that would shoot up from the smooth lawn outside the gallery to a height of 16m. His youngest son Samuel, recently qualified as an architect and now working in his office, looked at the result and asked why he didn't do something a bit wilder.

"I had to go away for work, and when I came back he had hung these butterflies flying through the model - I thought that was really fantastic, so that's the effect we've tried to get with the roof."

The whole design duly got a twist, the massive glass roof sections apparently tilting and sliding, the huge timber beams canted as if about to roll off their supporting columns. It was the job of Ed Clark of Arup Engineering to make sure it stood up: "tricky", he said yesterday, sucking his teeth like any jobbing builder asked for an estimate.

Like its predecessors, the space will function as a cafe by day and a party and events space by night. Standing under an umbrella, occasionally sneezing gently, Gehry admitted yesterday that he had perhaps not fully considered the celebrated English summer. An earlier stage of the design had tarpaulin covers that could be pulled over the frame to give some shelter. "They may have to go back," he said, sighing.